Fishing nets for cultivation, fixed nets, materials such as ropes supporting them, nets for preventing jellyfishes, etc., from invading into an inlet of seawater for cooling, and screens for preventing sea pollution used under such as coast constructions are soaked in the sea for a long term and thus impregnated with seawater for a long term. Because thus stained by adhesive sea organisms, there are problems arise such as blockade of the mesh of a net, infectious disease or parasitical disease of various fishes caused by decreased seawater inflow, and damage or decreased buoyancy of the materials caused by increased weight of the net.
To prevent the net from being stained by adhesive sea organisms, currently a sea stainproofing treatment agent containing an organic tin compound, for example, TBT (tributyl tin compound) as an active ingredient, has been widely used. Use of it, however, is being controlled due to suspicion of accumulation of the active ingredient in environment.
On the other hand, as a stainproofing treatment agent not containing the organic tin compound, (a) Japanese Patent Publication No. 43962/1987 discloses use of a dialkylsulfide compound as an active ingredient and (b) Japanese Patent Laid-open No. 38306/1985 discloses a stainproofing agent for fishing nets containing tetraalkylthiuramdisulfide, dialkylpolysulfide, and 2-(thiocyanomethylthio)benzothiazole, etc., as active ingredients.
Furthermore, besides the above prior art, the present inventors suggest (c) a stainproofing agent for fishing nets containing a copolymer having specific hydrophilicity and thiocyanoalkylthiobenzoheterozole in Japanese Patent Laid-open No. 178562/1989.
Effective stainproofing cannot be obtained with only the dialkylsulfide compound disclosed in the above (a), and although tetraalkylthiuramdisulfide, dialkylpolysulfide and 2-(thiocyanomethylthio)benzothiazole disclosed in the above (b) have sufficient stainproofing for a short term, use of them alone does not allow active ingredients to elute in a sufficient amount from a treatment agent for fishing nets for a long term. Furthermore, it was found that only the copolymer having specific hydrophilicity and thiocyanoalkylthiobenzoheterozole suggested in the above (c) by the present inventors, are obviously not adequate to keep stainproofing in effect for a long term.
An object of the present invention is to provide a method for controlling the elution rate of a stainproofing agent eluting from fibriform or corded materials, which are treated with a sea stainproofing treatment agent, necessarily and sufficiently for a long term.